Editing How do turn signals work? (section)
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==Turn signal system troubleshooting== ===Single lamp failures=== This is one of the most common failures found on vehicle lamp systems. The first thing to do is check the bulb. If the bulb is good, check for power at the socket. ====How to check for power at the socket:==== #Get your DVOM out, set it for volts scale, V X 50 or higher, and turn the key on then the offending signal. #Carefully insert the probe of your meter into the socket, to the contact pad (S) on the bottom of the socket, and the other to a good ground. #If you read 0, then 12 volts then 0 again (flash signal), the power to the lamps and the system are working fine. You have a bonding issue. #Shut off power to the system, and key, and return to the offending socket. New cars today have plastic bumpers and anti-collision systems. Proper ground bonding is becoming scarce compared to bygone days. Also, lighting systems have had to rely on wired or remote location grounds. It is quite common to lose ground to a single socket and disable it. Set your meter for OHMS Scale, R X 1, calibrated 000, and measure between the socket and a known good ground. Your reading here must be 000, if infinite, or random, you need to perform good bonding repairs to the socket. Using a good contact cleaner, carefully clean the socket, pads and lamp brass base and its pads. Next, recheck the socket for bonding, if your readings are still infinite or random, replace the ground wire to a known good ground area. Use a star washer and burnish all the paint and dirt from the bonding area. That will get a single lamp back to operation. ===Dead system=== If none of the turn signal functions work at all, follow the steps below. #Pull the fuse, and with your DVOM, measure it on ohms scale, R X 1 , calibrated 000. #If it reads infinite, it is open. Replace the fuse and test the signal system again. If it reads 000, it is good, put it back in the buss box. #Next, set your meter to DCV, V X 50 or auto range, turn the key on, and remove the flasher. Place the black probe on ground, the the other into either of the two flasher terminals. One will read infinite, the other should read 12 volts. If you have that, power is good to the flash unit. #Next, set your meter to ohms, RX1 scale and measure across the pins or wires. Repair or replace as required. #If you don't have either a cut condition, or a burned socket, and still dead, check any lead front, or rear of the selected side. It should have 12 volts, either steady or intermittent on it. If not, your trouble is in the column harness between the plug and the switch. Or, the switch itself is bad. Repair or replace as required. ===Front signals work, but rear signals are dead (or vice-versa)=== #Isolate the two wires on the effected end from the column plug. Using your voltmeter, set to the above parameters, select a side, and measure the wire from the plug. It should show 12 volts (solid or intermittent). If the socket ground and a known good ground. If it shows 12 volts, you may have an open ground wire. Replace or install a ground from each socket to a hard frame ground, following proper bonding procedures (star washers and burnishing). ===Left or right side turn signals dead=== Follow the same procedure as outlined for front or rear dead above. However, apply it to the affected side. ===All rear turn signals flashing=== Inspect the turn signal switch for a short between the brake lamp circuit and the signal circuit. Check the column plug and harness for shorts. Ohm the harness out with no power on, but either side selected. You should have no reading from the selected side to the brake lamp circuit, and continuity in the "Off" position to the brake lamps. If not, inspect the switch and harness, and repair or replace as needed.
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